1. Technical Field
The present invention relates to a gas turbine. Priority is claimed on Japanese Patent Application No. 2012-160904, filed Jul. 19, 2012, the content of which is incorporated herein by reference.
2. Background Art
A gas turbine includes a compressor which compresses air for combustion, a combustor which injects a fuel into the air compressed by the compressor and burns the fuel, and a turbine which is driven by a high-temperature combustion gas burned by the combustor. In the gas turbine, cavities are often defined such as between respective modules of the combustor and the turbine, between respective modules of a high-pressure turbine and a low-pressure turbine included in the turbine, and between shrouds disposed at vanes of the turbine and platforms and shrouds disposed at blades.
The cavity communicates with a main flow passage of the gas turbine in which the combustion gas flows, and the combustion gas of the main flow passage is entrained. Because the combustion gas is flowed into the cavity due to the entrainment of the combustion gas, the flow rate of the combustion gas flowing in the main flow passage is lowered, and thereby the efficiency of gas turbine is decreased.
When the combustion gas is flowed into the cavity, the temperature of inner parts such as a turbine disc increases, shortening the life of the parts. Thereby, a method of suppressing the rise in temperature of the inner parts of the cavity may be considered by increasing the flow rate of cooling air that cools the inner parts in the cavity. However, if the flow rate of the cooling air increases, the cooling air mixed in the combustion gas increases, which decreases the efficiency of gas turbine.
Japanese Patent No. 3226543 discloses a structure in which a clearance of an opening portion is narrowed as much as possible by installing a knife edge seal in end portions of platforms of blades facing shrouds of vanes, whereas disposing an abradable surface in the end portions of the vanes facing the knife edge seal, in order to prevent a working fluid which is the combustion gas from entering the cavity.
Further, Japanese Unexamined Patent Application, First Publication No. 2009-97396 discloses that an opening portion of a cavity approaching a main flow passage is made in a labyrinth structure, in order to prevent the combustion gas from entering the cavity.
However, in the above-mentioned gas turbine, for example, the end portions of the shrouds of the vanes and the end portions of the platforms of the blades may come in contact in the opening portion of the cavity, if so-called thermal extension due to a thermal expansion occurs when the clearance of the opening portion of the cavity is made small. In efforts to reduce the entrainment of combustion gas while allowing thermal extension, the structure of the cavity opening may become complicated.
Further, when the opening portion of the cavity is designed such that contact by the thermal extension is allowed therein, the exchange of worn parts, or the like may become necessary and the frequency of maintenance may increase.